The invention relates to catalytic converter monitoring systems of internal combustion engines responsive to exhaust gas oxygen sensors before and after the catalytic converters.
To meet current emission regulations, automotive vehicles must have on-board diagnostic systems to detect the malfunction of any component of the emission system, including a catalytic converter. A vehicle containing more than one catalytic converter may monitor each catalytic converter to guarantee detection of degraded system performance. An example would be that of a vehicle containing a V-type engine where catalytic converters coupled near or close to the engine are used. In this system, each catalytic converter may be monitored to determine emission compliance.
Catalytic converter monitoring systems are known in which an upstream and a downstream exhaust gas oxygen sensor are compared to give an indication of catalytic degradation. If sufficient degradation occurs, these systems will diagnose the deteriorated performance and illuminate a malfunction indicator. As a result, a new catalytic converter will be required. In the example of a V-type engine using two close coupled catalytic converters, each being monitored, when the measured performance of either of the two catalytic converters falls below a predetermined threshold, a malfunction is indicated. An example of such an approach is disclosed in U.S. Pat. No. 5,357,751.
The inventors herein have recognized numerous problems with the above approach. For example, in systems containing a dual bank engine connected to two monitored catalytic converters, the catalytic converters may not age at the same rate. Thus, one catalytic converter may have degraded past a threshold indicating possible reduced performance while the other is operating with much higher performance. While the total emissions of the vehicle are still within allowable amounts, a malfunction is indicated because one of the catalytic converters has degraded much faster than the other.
An object of the invention claimed herein is to provide a catalytic converter monitoring method capable of accounting for variations in catalytic converter aging between two converters, each coupled to separate engine banks.
The above object is achieved, and problems of prior approaches overcome, by the method shown in claim 1. In one particular aspect of the invention, the method comprises measuring a first number of transitions from a first state to a second state of a first exhaust gas oxygen sensor upstream of the first catalytic converter, measuring a second number of transitions from said first state to said second state of a second exhaust gas oxygen sensor downstream of the first catalytic converter, measuring a third number of transitions from said first state to said second state of a third exhaust gas oxygen sensor upstream of the second catalytic converter, measuring a fourth number of transitions from said first state to said second state of a fourth exhaust gas oxygen sensor downstream of the second catalytic converter, and determining a degradation of the first and second catalytic converters derived from a combination of a first ratio between said first and second number of transitions and a second ratio between said third and number of transitions.
By using a combination of the first ratio and second ratio, a total system performance can be inferred, leading to more accurate catalytic converter monitoring. For example, when the first upstream and first downstream exhaust gas oxygen sensors are coupled to one bank of an engine and the second upstream and second downstream exhaust gas oxygen sensors are coupled to another bank, the combination of the first and second ratios can detect when the catalytic converters are aging unequally. This information can be used to provide a malfunction indication when the total system degradation has reached a predetermined level.
An advantage of the present invention is the ability to more accurately determine the total catalytic converter system performance for systems having multiple converters.
Another advantage of the present invention is the reduction in false malfunction indications.
Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification.